1. Field of the Invention
The present invention relates to a rocker arm for opening and closing a valve disposed on a cylinder head in accordance with the sliding operation of a can.
2. Description of the Related Art
Conventionally, there is known a rocker arm which is made by casting according to a lost wax process. However, since the thus-cast rocker arm is great in weight, there is proposed a rocker arm which is made of a metal plate and is thereby reduced in weight (For example, see patent literature 1.).
Here, FIGS. 8 to 10 show an example of a conventional metal-plate-made rocker arm 81 of an end pivot type.
The rocker arm 81 comprises a main body 82, a support shaft 83, a roller 64, and a plurality of needle-shaped rollers 85.
The main body 82 includes a pair of side walls 86, 87, a pivot portion 88 with which a rush adjuster can be contacted, and a valve stem guide portion 89 with which the stem end of a valve can be contacted. Between the pair of side walls 86, 87, there is interposed the support shaft 83 so as to extend between them; and, on the outer periphery of the support shaft 83, there is rotatably supported the roller 84 with which a cam can be contacted through the plurality of needle-shaped rollers 85.
[Patent Literature]
JP-Application-9-91831
In the case of the conventional metal-plate-made 10 rocker arm 81, the pivot portion 88 is formed integrally with the pair of side walls 86, 87, whereas the valve step guide portion 89 is produced as a separate member and is then laser welded to the pair of side walls 86, 87.
As described above, since the pivot portion 88 is formed integrally with the pair of side walls 86, 87, the thickness of the periphery of the pivot portion 88 can be reduced, thereby being able to reduce the weight of the rocker arm 81 accordingly.
However, the weight of the periphery of the valve stem guide portion 89 is large due to the laser welding, so that the position of center-of-gravity of the rocker arm 81 becomes near to the valve stem guide portion 89.
Because the position of center-of-gravity of the rocker arm 81 is made to lie near to the valve stem guide portion 89, the moment of inertia around the pivot portion 88 serving as a fulcrum is large, which lowers the response performance of the rocker arm 81 when it is in use.